Based on the underpass project between Fuzhou Railway Station of Binhai Express and transfer hub, the multi-step mortar filling scheme (scheme A) and one-step mortar filling scheme (scheme B) for the construction of pipe roof crossing over existing line are proposed. The whole construction process of pipe roof is simulated on the ABAQUS platform, and the vertical displacement and convergence of the existing line and the surface settlement are well focused. The simulation results show that the vertical displacement of existing line tends to settle gradually in scheme A, while tends to float and then settle suddenly in scheme B. However, the final vertical displacement caused by the two schemes is roughly the same. The distribution of surface settlement shows an irregular trough in both two schemes. The maximum settlement is located on the left axis of box-typed pipe roof, and scheme B is slightly smaller than scheme A. Considering the influence of existing line and construction efficiency, the scheme B is adopted for the pipe roof construction on site. The field monitoring for vertical displacement of existing line and surface settlement are also conducted, and the monitoring data accord with numerical simulations roughly. These researches can provide some reference for the pipe roof construction on similar scenario.